Physical Properties of Soil Denham Springs Freshman High Ag I

Terminology Texture – physical property of soil referring to the relative amounts of sand, silt, and clay; how a soil feels. Sand – largest individual soil particle Silt – medium sized individual soil particle

Terminology Clay – smallest individual soil particle Peds – natural grouping of soil particles Clods – artificial grouping of soil particles Infiltration – movement of water into the soil

Terminology Mechanical analysis – process of separating a soil into its various parts to permit study. Mottlings – indication of internal drainage & aeration; soil exhibits spots of color. Percolation – movement of water through the soil. Permeability – characteristic of soil which permits variations in the speed of air & water movement.

Texture At the most basic level, soil texture can be determined by feel & described as one of the following: –Coarse –Moderately Coarse –Medium –Moderately Fine –Fine

Specific Soil Textures (from Coarsest to Finest) determined by Mechanical Analysis Sand (Coarse) Loamy Sand (Moderately Coarse) Sandy Loam (Moderately Coarse) Loam (Medium) Silt Loam (Medium) Silt (Medium) Sandy Clay Loam (Medium)

Specific Soil Textures continued (from Coarsest to Finest) Clay Loam (Moderately Fine) Silty Clay Loam (Moderately Fine) Sandy Clay (Moderately Fine) Silty Clay (Fine) Clay (Fine)

Specific Soil Textures determined by Feel Sand – Dry = no clods. Moist = easily crumbled ball, does not ribbon, does not stain fingers. Loamy Sand – Dry = very weak clods. Moist = easily crumbled ball, does not ribbon or stain fingers.

Felt textures cont… Loam (most difficult) – Dry = clods slightly hard to break. Moist = forms firm ball, ribbons poorly, poor fingerprint Silt – Dry = clods moderately difficult to break; ruptures suddenly. Moist = Smooth, slick feel; forms firm ball, slight ribbon; good fingerprint.

Felt textures cont… Silt Loam – Dry = clods moderately difficult to break; ruptures suddenly. Moist = Smooth, slick feel; forms firm ball, slight ribbon; good fingerprint. Sandy Clay Loam – Dry = clods break with some difficulty. Moist = forms firm ball that dries moderately hard; ½” ribbon.

Felt Textures cont… Clay Loam – Dry = clods break with difficulty. Moist = forms firm ball that dries moderately hard; ½” ribbon. Silty Clay Loam – Dry = resembles clay loam, only stickier. Moist = shows good fingerprint; forms firm ball drying moderately hard. ½” thin ribbon.

Felt Textures continued… Sandy Clay – Dry = clods broken with extreme pressure. Moist = forms very firm ball drying quite hard. Thin, long, somewhat gritty ribbon. Silty Clay – Dry = clods broken with extreme pressure. Moist = forms very firm ball drying quite hard. Thin, long, smooth ribbon. Clay – Dry = clods often can’t be broken. 2”-3” ribbon

13 Particle Size of Some Soils

14 Well sorted fine sand Poorly sorted silty fine to medium sand Particle Size Distribution Particle size distribution curves –Relative % of grain sizes Soil classification standards Soil texture

15 Particle Size Distribution Sand49% Clay40% Soil Characteristics of Cyprus Soil Sample

Porosity –property of the interstices of the porous medium –percent of total volume occupied by void space

Porosity solid Pore with air Pore with water Soil volume V (Saturated) Soil volume V (Unsaturated) Porosity: total volume of soil that can be filled with water

18 Typical Values of Porosity MaterialPorosity (%) Peat Soil60-80 Soils50-60 Clay45-55 Silt40-50 Med. to Coarse Sand35-40 Uniform Sand30-40 Fine to Med Sand30-35 Gravel30-40 Gravel and Sand30-35 Sandstone10-20 Shale1-10 Limestone1-10

Soil Structure Structure is the way individual soil particles are grouped together. Types of Structure –Blocklike – peds look like irregular shaped cubes. –Platy – peds appear flattened in overlapping horizontal sheets.

Structure continued.. –Prismatic – peds are long vertical columns without rounded tops. –Spheroidal – peds are somewhat rounded, granular, and crumbly. –Structureless – Either single grained or solid & massive; no noticeable peds.

Why structured soils are good Easier to cultivate Permits greater water intake Does not restrict root growth Encourages better drainage Allows oxygen to enter the pores Helps organic decomposition and release of plant nutrients

Soil structure is fragile. Soil structure can be damaged or destroyed by: –Working soil that is too wet –Repeated movement of heavy objects or animals over the soil –Use of equipment at the same depth of the soil –Continual flooding of the soil

Improving soil structure Leave it alone. Given enough time nature will repair damaged structure Planting green manure crop Incorporate plant residue into the soil

Infiltration & Percolation Rates The rate that water enters (infiltrates) a soil and then moves through the soil profile (percolates) depends partly on soil structure. –Rapid infiltration with granular and loose, single grained structureless soil. –Moderate infiltration with blocklike and prismatic structure. –Slow infiltration with platy and solid, massive structureless structure.

Internal Drainage If permeability is slow or very slow, water stays in the pore spaces and air cannot enter. Soils with poor internal drainage and aeration are mostly gray with some red or yellow streaks. Soils with fair to good internal drainage and aeration are yellow-brown or reddish- brown with some gray spots (mottlings)

Traffic Pans Area of soil compaction and root restriction, usually in the topsoil. Caused by heavy traffic (vehicles, animals, &/or people) over the same area –Reduces the movement of air, water, & roots –Detrimental to plants –May also affect runoff and erosion

Alleviating Traffic Pans Stay on sidewalks &/or paved areas Subsoiling No-till, reduced tillage, or minimum tillage plans